1. Field of the Invention
The present invention relates to a sodium-intervened superconductor and its manufacturing method and more particularly, to the sodium-intervened superconductor expressed by the following Formula 1 and its manufacturing method, wherein the superconductor, prepared from a stoichiometric mixture of Y.sub.2 O.sub.3, NaCuO.sub.2, BaCuO.sub.2, Ln.sub.2 O.sub.3 (Ln:Lanthanide ion) and CuO under the atmosphere of oxygen, has some advantages in that a) through the use of NaCuO.sub.2, a ternary oxide, as a reactant, the formation of impurities and sodium evaporation may be prevented, and b) through partial substitution of a divalent barium by a trivalent lanthanide ion, the superconductor is thermally stable in air with a higher critical current density (J.sub.c) and critical temperature (T.sub.c):
Formula 1 EQU (Na.sub.1-y Y.sub.x)(Ba.sub.1-y Ln.sub.y).sub.2 Cu.sub.3 O.sub.6+.delta.
wherein, Ln is a trivalent lanthanide ion other than Ce and Pr; 0.1&lt;x&lt;0.9; and 0.1&lt;y&lt;0.3.
2. Description of the Related Art
Superconductivity was discovered from mercury (Hg) by H. Kamerlingh Onnes for the first time in 1908, which is the phenomenon to lose electric resistance when some specific metal or alloy is cooled below certain temperature. The transition temperature is defined as the superconducting critical temperature (T.sub.c). Such superconductivity may be found from nearly all metals at sufficiently low temperature but not limited to a few metals, while its temperature may vary depending on the kinds of metal. For example, the T.sub.c of mercury for superconductivity is 4 K and that of an alloy comprising both tin and niobium is 18 K. Besides the metal and intermetallic compounds, the first high temperature oxide superconductor, La.sub.2-x M.sub.x CuO.sub.4, was invented by Bednorz and Muller in 1986. Since then, a variety of superconductors having higher T.sub.c than liquid nitrogen (boiling point: 77 K) have been successfully synthesized, which is a turning point for the applied studies of superconductivity; among them, YBa.sub.2 Cu.sub.3 O.sub.7-.delta., Bi.sub.2 Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.10, Tl.sub.2 Ba.sub.2 Ca.sub.2 Cu.sub.3 O.sub.10 and HgBa.sub.2 Ca.sub.2 Cu.sub.3 O.sub.8+.delta. a superconductors are typical.
However, the superconductors other than YBa.sub.2 Cu.sub.3 O.sub.7-.delta. have faced some difficulty in application due to their toxicity and volatility. Even in the yttrium-based superconductor (YBa.sub.2 Cu.sub.3 O.sub.7-.delta.), it has also recognized some disadvantage in that its superconducting property is drastically changed by the oxygen content.